In control systems for devices such as robots in factory automations (FA), safety is important, and it is necessary to stop the devices when anomaly is detected. If the systems are operating properly, it is possible to stop the devices by outputting commands to stop the operations to the devices. However, if anomaly occurs in the systems, even if the commands to stop the operations are output to the devices, it is not certain whether the instructions will be properly executed. Safety control devices are thus sometimes used to control switches that connect the devices to electric power sources, to stop supply of power to the devices by turning off the switches and forcibly stop the operations of the devices.
Generally, safety control devices are configured to perform dual judging of commands input from the outside. If the two judgment results agree with each other, the safety control devices exercise control based on the input command. If the two judgment results do not agree with each other, the safety control devices exercise safety control (i.e., to stop the devices in these situations) to improve the safety.
The performance of a safety control device is determined by the response time between a time point at which safety can no longer be confirmed and a time point at which a device is stopped. Thus, shortening a processing time period between reception of a command and output of an output signal to stop the device leads to improvement in the performance of the safety control device.
An example of a conventional technique to increase the speed of the dual control process is disclosed in Patent Document 1. In Patent Document 1, the technique in a dual control apparatus having two multi-processor-type controlling devices disposed in parallel is disclosed, in which functions of computing controllers and input/output controllers are distributed among different CPU elements, and input/output data comparing processes performed by the dual input/output controllers are performed concurrently with data transfer, so that detection of disagreement between the two systems is performed in a short period of time.                Patent Document 1: Japanese Patent Application Laid-open No. S59-43450        